[PATCH] x86: Make stringop_algs::stringop_strategy ctor constexpr [PR100246]

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Jul 06, 2021 at 11:17:55AM +0100, Iain Sandoe wrote:
> >> The addition of the CTOR is the fix for the C++ compile fail in the PR, the conditional is
> >> only there because the same header is compiled by C and C++.
> > 
> > Whoops sorry - I was confused.  The patch looks OK to me if you add a comment
> > before the CTOR why it was added (maybe quoting the error that happens)
> 
> Thanks, pushed as below.
> Iain
> 
> -------
> 
> X86: Provide a CTOR for stringop_algs [PR100246].
> 
> Several older compilers fail to build modern GCC because of missing
> or incomplete C++11 support.
> 
> Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
> 
> PR bootstrap/100246 - [11/12 Regression] GCC will not bootstrap with clang 3.4/3.5 [xcode 5/6, Darwin 12/13]
> 
> 	PR bootstrap/100246
> 
> gcc/ChangeLog:
> 
> 	* config/i386/i386.h (struct stringop_algs): Define a CTOR for
> 	this type.

Unfortunately, as mentioned in my
https://gcc.gnu.org/pipermail/gcc-patches/2021-November/583289.html
mail, without the new dyninit pass this causes dynamic initialization of
many variables, 6.5KB _GLOBAL__sub_I_* on x86_64 and 12.5KB on i686.

The following so far only lightly tested patch makes the ctor constexpr
so that already the FE is able to statically initialize all those.

I don't have access to Darwin nor to the broken versions of clang, do you
think you could test bootstrap there with this too?
Especially because 11.x is not going to have the dyninit optimization for
sure, it would be nice to do this on the 11 branch too.

2021-11-04  Jakub Jelinek  <jakub@redhat.com>

	PR bootstrap/100246
	* config/i386/i386.h
	(stringop_algs::stringop_strategy::stringop_strategy): Make the ctor
	constexpr.

--- gcc/config/i386/i386.h.jj	2021-09-28 23:18:35.282563395 +0200
+++ gcc/config/i386/i386.h	2021-11-04 10:48:47.165086806 +0100
@@ -78,8 +78,9 @@ struct stringop_algs
        this issue.  Since this header is used by code compiled with the C
        compiler we must guard the addition.  */
 #ifdef __cplusplus
-    stringop_strategy(int _max = -1, enum stringop_alg _alg = libcall,
-		      int _noalign = false)
+    constexpr stringop_strategy(int _max = -1,
+				enum stringop_alg _alg = libcall,
+				int _noalign = false)
       : max (_max), alg (_alg), noalign (_noalign) {}
 #endif
     const int max;

	Jakub